Microwave ovens and furnaces have been known for some time. In many house hold microwave ovens, the microwaves are generated in an enclosed heating compartment made of a microwave reflective material such as steel or aluminum. The microwaves are retained in the compartment and are eventually absorbed by the microwave absorptive materials placed within the compartment. In commercial scale units, the microwave energy is generated by a separate microwave generator and then channeled into the separate heating compartment via a microwave waveguide. The waveguide generally comprises a conduit made of a microwave reflective material. Uniform heating of the material is assisted by the inclusion of devices for rotating or agitating the material.
To permit the continuous heating of granular material, microwave ovens have been made having a long microwave transparent conduit, part of which is contained within the microwave reflective heating compartment. The material to be heated is then passed through the conduit, and as it passes through the portion of the conduit contained in the heating compartment, the material is exposed to microwaves. This arrangement permits the uninterrupted flow of material through the microwave reflective heating chamber. However, since the microwave transparent conduit must enter and exit the microwave reflective heating chamber, there is always the possibility that microwave energy will escape the heating chamber by exiting at the point where the conduit meets the walls of the heating chamber. To minimize this leakage, the diameter of the microwave transparent conduit must be minimized. This design limitation restricts the maximum flow-through rates of this type of microwave oven. Furthermore, since the consequences of leaked microwaves are graver where high intensity microwaves are required, this basic design effectively limits the maximum microwave intensities that can be safely used, and therefore, the maximum heating temperatures possible. Finally, the limitations placed on this design of microwave ovens greatly limits the versatility of the oven. Usually, each oven is designed with a particular sized conduit in mind to accommodate a particular flow rate and heating temperature for any given material. There is a need for a versatile and safe continuous flow microwave oven that can operate at high temperatures and high flow rates.